This invention relates to a method of making an injection molding nozzle with an improved terminal for the electric heating element.
Nozzles with integral heating elements are well known in the art. For example, the applicant's Canadian patent application Ser. No. 542,185 entitled "Coated Injection Molding Nozzle and Method" filed July 15, 1987 and U.S. application Ser. No. 086,621, filed Aug. 18, 1987 disclose a nozzle in which the forward end of the heating element extends into the nose portion. The applicant's Canadian patent application Ser. Nos. 549,518 entitled "Injection Molding Nozzle Having Grounded Heating Element Brazed into Pointed Tip" and 549,517 entitled "Method of Manufacture of Injection Molding Nozzle Having Grounded Heating Element Brazed into Pointed Tip" both filed Oct. 16, 1987 disclose further improvements. The electrical heating element normally has a resistance wire extending centrally through an electrical insulating material such as magnesium oxide inside a steel casing. As is well known, it is necessary to connect the resistance wire at the rear end or ends of the heating element to a larger diameter conductor to form a "cold terminal" to which an external electrical lead is connected. In instances where the heating element is cast or brazed in place it may also be necessary to seal against leakage of the brazing material.
In the past, a variety of different structures have been used to provide the electrical terminal. For instance, the applicant's U.S. Pat. Nos. 4,403,405 entitled "Sprue Bushing Connector Assembly Method" which issued Sept. 13, 1983 and 4,446,360 (divisional) entitled "Sprue Bushing Connector Assembly" which issued May 1, 1984 disclose connectors using crimping sleeves and sealing using a split washer arrangement. Other arrangements using sleeves are shown in the applicant's U.S. Pat. Nos. 4,557,685 entitled "Heated Nozzle for Injection Molding Apparatus" which issued Dec. 10, 1985 and 4,583,284 (divisional) entitled "Method of Manufacture of Injection Molding Heated Nozzle with Brazed in Heating Element" which issued Apr. 22, 1986, as well as in the applicant's Canadian patent application Ser. No. 532,677 entitled "Injection Molding Nozzle and Method" which was filed Mar. 20, 1987. However, all of these prior art heating element terminals have the disadvantages that they are made complete prior to assembly and relatively difficult to adjust to the right overall length consistently for uniform temperature control when in operation.